The DNA Chain of TraditionThe Discovery of the "Cohen Gene"

by Rabbi Yaakov Kleiman

Jewish tradition, based on the Torah, is that all Kohanim are direct descendants of Aharon, the original Kohen. The line of the Kohanim is patrilineal: it has been passed from father to son without interruption from Aharon, for 3,300 years, or more than 100 generations.

Dr. Karl Skorecki was attending services one morning. The Torah was removed from the ark and a Kohen was called for the first aliya. The Kohen called up that particular morning was a visitor: a Jew of Sefardic background. His parents were from Morocco. Skorecki also a has a tradition of being a Kohen, though of Ashkenazi background. His parents were born Eastern Europe. Karl (Kalman) Skorecki looked at the Sefardi Kohen's physical features and considered his own physical features. they were significantly different in stature, skin coloration and hair and eye color. Yet both had a tradition of being Kohanim--direct descendants of one man--Aharon HaKohen.

Dr. Skorecki considered, "According to tradition, this Sefardi and I have a common ancestor. Could this line have been maintained since Sinai, and throughout the long exile of the Jewish people?" As a scientist, he wondered, could such a claim be tested?

Being a nephrologist and a top-level researcher at the University of Toronto and the Rambam-Technion Medical Center in Haifa, he was involved in the breakthroughs in molecular genetics which are revolutionizing medicine and the study of the life-sciences. He was also aware of the newly developing application of DNA analysis to the study of history and population diversity.

He considered a hypothesis: if the Kohanim are descendants of one man, they should have a common set of genetic markers--a common haplotype-- that of their common ancestor. In our case, Aharon HaKohen.

A genetic marker is a variation in the nucleotide sequence of the DNA, known as a mutation. Mutations which occur within genes—a part of the DNA which codes for a protein—usually cause a malfunction or disease, and is lost due to selection in succeeding generations. However, mutations found in so-called “non-coding regions” of the DNA tend to persist.

Since the Y chromosome, besides for the genes determining maleness, consists almost entirely of non-coding DNA, it would tend to accumulate mutations. Since it is passed from father to son without recombination, the genetic information on a Y chromosome of a man living today is basically the same as that of his ancient male ancestors, except for the rare mutations that occur along the hereditary line. A combination of these neutral mutations, known as a haplotype, can serve as a genetic signature of a man’s male ancestry. Maternal geneaologies are also being studied by means of the m-DNA (mitrocondrial DNA), which is inherited only from the mother.

Dr. Skorecki then made contact with Professor Michael Hammer, of the University of Arizona, a leading researcher in molecular genetics and a pioneer in Y chromosome research. Professor Hammer uses DNA analysis to study the history of populations, their origins and migrations. His previous research included work on the origins of the Native American Indians and the development of the Japanese people.

A study was undertaken to test the hypothesis. If there were a common ancestor, the Kohanim should have common genetic markers at a higher frequency than the general Jewish population.

In the first study, as reported in the prestigious British science journal, Nature (January 2, 1997), 188 Jewish males were asked to contribute some cheek cells from which their DNA was extracted for study. Participants from Israel, England and North America were asked to identify whether they were a Kohen, Levi or Israelite, and to identify their family background.

The results of the analysis of the Y chromosome markers of the Kohanim and non-Kohanim were indeed significant. A particular marker, (YAP-) was detected in 98.5 percent of the Kohanim, and in a significantly lower percentage on non-Kohanim.

In a second study, Dr. Skorecki and associates gathered more DNA samples and expanded their selection of Y chromosome markers. Solidifying their hypothesis of the Kohens' common ancestor, they found that a particular array of six chromosomal markers were found in 97 of the 106 Kohens tested. This collection of markers has come to be known as the Cohen Modal Haplotype (CMH)--the standard genetic signature of the Jewish priestly family. The chances of these findings happening at random is greater than one in 10,000.

The finding of a common set of genetic markers in both Ashkenazi and Sefardi Kohanim worldwide clearly indicates an origin pre-dating the separate development of the two communities around 1000 C.E. Date calculation based on the variation of the mutations among Kohanim today yields a time frame of 106 generations from the ancestral founder of the line, some 3,300 years, the approximate time of the Exodus from Egypt, the lifetime of Aharon HaKohen.

Professor Hammer was recently in Israel for the Jewish Genome Conference. He confirmed that his findings are consistent that over 80 percent of self-identified Kohanim have a common set of markers. The finding that less than one-third of the non-Kohen Jews who were tested possess these markers is not surprising to the geneticists. Jewishness is not defined genetically. Other Y-chromosomes can enter the Jewish gene pool through conversion or through a non-Jewish father. Jewish status is determined by the mother. Tribe membership follows the father’s line.

Calculations based on the high rate of genetic similarity of today’s Kohanim resulted in the highest “paternity-certainty” rate ever recorded in population genetics studies—a scientific testimony to family faithfulness.

Wider genetic studies of diverse present day Jewish communities show a remarkable genetic cohesiveness. Jews from Iran, Iraq, Yemen, North Africa and European Ashkenazim all cluster together with other Semitic groups, with their origin in the Middle East. A common geographical origin can be seen for all mainstream Jewish groups studied.

This genetic research has clearly refuted the once-current libel that the Ashkenazi Jews are not related to the ancient Hebrews, but are descendants of the Kuzar tribe--a pre-10th century Turko-Asian empire which reportedly converted en masse to Judaism. Researchers compared the DNA signature of the Ashkenazi Jews against those of Turkish-derived people, and found no correspondence.

In their second published paper in Nature (July 9,1998) the researchers included an unexpected finding. Those Jews in the study who identified themselves as Levites did not show a common set of markers as did the Kohanim. The Levites clustered in three groupings, one of them the CMH. According to tradition, the Levites should also show a genetic signature from a common patrilineal ancestor.

It is interesting to note that the tribe of Levi has a history of a lack of quantity. The census of BaMidbar shows Levi to be the smallest of the tribes. After the Babylonian exile, the Levites failed to return en masse to Jerusalem, though urged by Ezra HaSofer to do so. They were therefore fined by losing their exclusive rights to maaser. Though statistically, the Levites should be more numerous than Kohanim, today in synagogue, it is not unusual to have a minyan with a surplus of Kohanim and yet lack even one Levite. The researchers are now focusing effort on the study of Levites' genetic make up to learn more about their history in the Diaspora.

Using the CMH as a DNA signature of the ancient Hebrews, researchers are pursuing a hunt for Jewish genes around the world. The search for lost tribes, whether the biblical 10 Lost Tribes which were uprooted from Eretz Yisrael by the Assyrians, or other would-be Jews, Hebrews or "chosen peoples," is not new. Using the genetic markers of the Kohanim as a yardstick, these genetic archaeologists are using DNA research discover historical links to the Jewish people.

Many individual Kohanim and others have approached the researchers to be tested. The researchers' policy is that the research is not a test of individuals, but an examination of the extended family. Having the CMH is not a proof of one's being a Kohen, for the mother's side is also significant in determining one's Kohanic status. At present, there are no halachic ramifications of this discovery. No one is certified nor disqualified because of their Y chromosome markers.

The research, which began with an idea in shul, has shown a clear genetic relationship amongst Kohanim and their direct lineage from a common ancestor. The research findings support the Torah statements that the line of Aharon will last throughout history. That our Torah tradition is supported by these findings should be a reinforcement for Kohanim and for all those who know that the Torah is truth, and that God surely keepsHis promises.

May we soon see Kohanim at their service, Levites on their Temple platform and Israelites at their places.

A Blessing Forever

Just as the Kohanim’s lineage spans more than 3,000 years, so does the Blessing which they deliver span Jewish history. Since it’s inception at the inauguration of the Mishkan on Rosh Chodesh Nissan, 2449 CC (equals 1311 BCE), the Blessing of the Kohanim has been recited daily by descendants of Aharon HaKohen somewhere in the world, everyday.

It is a remnant of the Temple service which was never lost. After the destruction of the Second Temple in 70 CE, the mishmarot—family service groups of Kohanim—kept their tradition of knowing the week of their particular watch at the Temple. From the time of the Babylonian and Persian exile, Jewish communities have included the Birkat Kohanim in their communal service.

Sefardic custom, as written in the Shulchan Aruch, is for the Kohanim to bless the congregation everyday. Following the Rema, the Ashkenazi custom became to perform the Blessing only on holidays. Presently in Eretz Yisrael, following the talmidim of the Vilna Gaon, the custom has been restored to recite the blessing everyday and twice on Shabbat, Rosh Chodesh and Yom Tov.